Researchers from the Institute of Archaeology and Ethnology of the Polish Academy of Sciences in Warsaw checked the area of approximately 50 square kilometres near Chełmno, northern Poland.

After analysing the results of aerial laser scanning, they selected a number of then unknown archaeological sites. In late 2018, they identified over a dozen sites, including the remains of four castles, embankments several hundred meters long and mound graves.

Constructions were detected in a forest area, which was, until now, poorly explored by researchers due to a lack of sufficient tools and the technology that would allow accurate exploration.

Scientists emphasise that finding burial mounds in this area is quite rare. The ages of the newly discovered mounds are not yet known.

"On the basis of the analysis of the historical road system, it is certain that the remains come from before the 18th century, which makes the finding even more puzzling," the project manager Jerzy Czerniec said.

This year, the archaeologists plan to conduct geophysical surveys of some of the most interesting sites. In late 2019, they aim to carry out the first excavations.

Apart from archaeologists, experts in other fields of science are also involved in the search, including specialists in soil science and landscape shaping.